Occupying this pedestal might have made her insufferably pompous, pathologically reclusive, or both. Not a bit of it: Iris was friendly, down-to-earth and rather jolly. She and her husband John Bayley were by this point inseparable, growing old together in the manner described in Iris: A Memoir and depicted in the subsequent film. If Iris was no longer a wanderer in the wilderness on a quest for truth, beauty and the good, with an insatiable appetite for erotic adventure, she was still the composer of lyrical novels of ideas, the mistress of metaphysics, the virtuoso of virtue.

The last time I spent time with her, at a literary festival in the early 1990s, she was already suffering from the dementia that ultimately rendered the incomparable instrument of her mind incapable of performance. John unwisely let himself be persuaded by the festival director to coax Iris onto the platform for a debate. She could no longer cope with public speaking and her visible distress was excruciating to behold. But she still had moments of lucidity and her abiding emotion was that of gratitude. When I read aloud the greatest Holocaust poem in German, Paul Celan’s “Death Fugue”, to a disgruntled British audience, Iris said afterwards how much she had enjoyed the music of the verses, even though she was by then losing fluency in her own language. Iris was always grateful for small mercies, and her correspondence testifies to her overwhelming gratitude for love and companionship throughout her intellectual life.

Those letters have now appeared in a compulsively readable volume: Living on Paper: Letters from Iris Murdoch, 1934-1995, edited by Avril Horner and Anne Rowe (Chatto & Windus, 666pp, £25). Reflecting on her many affairs and friendships, one is driven to the conclusion that, for Iris, the most powerful aphrodisiac was genius. It worked both ways. She was so gifted that many of the most brilliant of her contemporaries of both sexes were drawn to her, but although she often reciprocated, she longed for the unattainable. Already in 1939, aged just 19, she wrote: “I find myself quite astonishingly interested in the opposite sex, and capable of being in love with about six men all at once — which gives rise to complications and distresses.” For Iris, love was a form of sentimental journey, an education in how to live. Each new man in her life — and there were often several at once — was an opportunity to experience the eroticism of intellectual discovery.

All her life, Iris found that, for her, love, sex and friendship were a single continuum, with no clear boundaries separating them. To the end, she was very much a “touchy-feely” person. In a self-revelatory letter in 1967 to Georg Kreisel, one of her few male friends who did not become her lover, she confessed that she was “probably not at all normal sexually. I am not a lesbian, in spite of one or two unevents on that front; I am certainly strongly interested in men. But I don’t think I want normal heterosexual relations with them. (It’s taken me a long time to find this out.) I think I am sexually rather odd, which is a male homosexual in female guise . . . I doubt if Freud knew anything about me, though Proust knew about my female equivalent. I have never been much good at going to bed, though quite often in love.”